This invention relates to video display apparatus. The invention also relates to a data processing system including a data processing unit and a video display device for displaying data from the processing unit.
More specifically, the invention is concerned with display apparatus in which the data to be displayed is stored in a display memory. During each cycle of operation, one processor access and a plurality of video accesses are made to the memory. During the processor access, the processing unit can update the data in the memory. In each video access, an item of data can be read out of the memory and fed to the display device.
A problem with this arrangement is that, because the processor access is interlaced with the video accesses, the video accesseses are skewed, i.e. they are all displaced towards one end of the cycle. Before the video data can be used by the display, it must first be de-skewed, to ensure that the data from the video accesses are available at equally spaced intervals. One way of doing this as described in U.S. Pat. No. 4 388 621 is to load the data from the video accesses into separate registers, and then to output the data from each of these registers in turn at equally spaced intervals.
One object of the invention is to provide an improved solution to the problem of de-skewing the video data.